The invention is directed to cutting inserts and, more particularly, to a cutting insert with a unique central cavity used to hold the insert within the pocket of a toolholder.
Cutting inserts are well known and a large percentage of them are of the throwaway design. Such inserts are detachably clamped on a toolholder and are removed from the toolholder and discarded when they become dull or chipped. Throwaway inserts are usually indexable so that an insert can be provided with at least two cutting edges for selective presentation to a workpiece. An indexable insert having multiple cutting edges is more economical because when one edge has been used, the insert may simply be indexed to the next usable edge. Such a feature is especially important when considering the high cost of materials from which inserts are produced.
In general, inserts must be securely and accurately held in place within an insert holder during the cutting operation. This is especially true when the inserts are deployed with numerically controlled machines which depend for accuracy upon an accurately located and firmly supported insert. When the inserts are large enough, it is possible to secure the insert both accurately and firmly within the pocket of a toolholder by providing the insert with a central hole and the toolholder with a pin-type clamping device. In other cases, such inserts may be held in place by a top clamp. Examples of such holders are found in U.S. Pat. Nos. 3,754,309; 3,399,442 and 3,762,005.
Whenever a central hole exists within an insert, the overall strength of the insert is somewhat reduced. The strength of the insert is reduced to a lesser degree whenever a cavity is placed within the insert for engagement by a top clamp. Nevertheless, whenever any material is taken from the insert body the insert, to some degree, weakens. The insert must, however, be secured within a toolholder and this typically requires the introduction of either a hole or a cavity within the insert to engage a pin through the insert or a clamp against the insert.
Cutting inserts for metalworking operations are typically made of wear-resistant material such as a hard cemented carbide or cermet comprised of tungsten carbide, titanium carbide, tungsten titanium carbide or TiC-TiN and a binder material such as cobalt, iron and/or nickel. The wear-resistant material may also be a tool steel or a ceramic material, such as aluminum oxide-based, silicon nitrate-based, or silicon-based ceramic materials.
It is an object of the subject invention to provide a central hole or cavity within an insert having a shape that permits the insert to be clamped in a variety of different index positions while minimizing the amount of material removed from the insert.
It is a further object of this invention to provide a plurality of clamping surfaces which may be as wide as possible within a given cavity.
Still other objects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
A cutting insert intended to be held within a toolholder by a clamp is comprised of a body of wear-resistant material. The body has a central longitudinal axis extending therethrough. The body also has a top surface and a bottom surface, a peripheral wall therebetween and a cutting edge formed by the intersection of the peripheral wall and the top surface. A central cavity extends within the top surface and has cavity walls defining a plurality of pairs of clamping surfaces. The clamping surfaces of a pair are separated from one another by a recess. In one embodiment, for a pair of clamping surfaces, the associated recess is preferably comprised of other clamping surfaces associated with different pairs of clamping surfaces.
The cavity has a perimeter and the perimeter preferably has the shape of an equilateral polygon. The recesses may be symmetrically positioned about the central longitudinal axis.
In an alternate embodiment, an indexable cutting insert intended to be held within a toolholder by a clamp is comprised of a body of wear-resistant material. The body has a central longitudinal axis extending therethrough. The body also has a top surface and a bottom surface, a peripheral wall therebetween, and a cutting edge formed by the intersection of the peripheral wall and the top surface.
A central cavity extends within the top surface and has cavity walls defining a plurality of pairs of clamping surfaces. The clamping surfaces of a pair are separated from one another by a recess. The perimeter of the cavity is preferably made up of two or more identical shapes superimposed upon one another and having as a common center point the central longitudinal axis.
Additionally, a toolholder assembly is comprised of a toolholder with a body having a pocket formed therein which has at least one side wall and a bottom wall. The assembly is further comprised of a cutting insert with an insert body having a top surface and a bottom surface with a peripheral wall therebetween. A cutting edge is formed by the intersection of the peripheral wall and the top surface. A central cavity extends within the top surface and has cavity walls defining a plurality of pairs of clamping surfaces, wherein the clamping surfaces of a pair are separated from one another by a recess. For each pair of clamping surfaces, the associated recess is comprised of other clamping surfaces associated with different pairs of clamping surfaces. The insert mounts within the toolholder pocket and a clamp mounted upon the toolholder having a protruding nose which engages a pair of the insert clamping surfaces and urges the insert into the pocket.